AlertDialog Button does not exist

Suddenly (without any changes in this project code) I started to obtained an error:

java.lang.RuntimeException: Unable to start activity ComponentInfo{<package>}: java.lang.IllegalArgumentException: Button does not exist

that error points to a method which wasn't yet called.

private void dialog(String title, String content){
    AlertDialog alertDialog = new AlertDialog.Builder(MainActivity.this).create();
    alertDialog.setTitle(title);
    alertDialog.setMessage(content);
    alertDialog.setCancelable(true);
    alertDialog.setButton(1, "OK", new DialogInterface.OnClickListener() {
           public void onClick(DialogInterface dialog, int which) {
               dialog.dismiss();
               }
            });
    alertDialog.show();
}

I tried to copy and use that code in other project - same result, and it was working not long ago (same target API etc.). Any idea what I'm overlooking?